Control apparatus

ABSTRACT

A control assembly to operate a gas oven. The main burner receives gas from a solenoid valve energized by a thermoelectric generator through a main thermostat switch. In order to reduce the oven temperature to, e.g. 170* F. to keep the food warm after a timer has run down, the timer and a keep-warm thermostat operate two switches, respectively, to short circuit the solenoid or the thermoelectric generator periodically. The thermoelectric generator output is in the millivolt region. Thus, use of one or two additional, inexpensive, series switches in the circuit can make solenoid operation unreliable because of even moderate contact resistance. Even the use of expensive gold may not avoid the series switch problem. The control assembly disclosed herein avoids this problem by use of a disabling shunt instead of a series switch.

United States Patent 1191 Saponara 1 Jan. 15, 1974 CONTROL APPARATUSPrimary Examiner-Herman J. Hohauser [75] Inventor. Domenlck Saponara,Macungle, Pa. y A. Donald Stolzy [73] Assignee: International Telephoneand Telegraph Corporation, New York, 57 1 ABSTRACT A control assembly tooperate a gas oven. The main [22] Filed: Feb. 20, 1973 burner receivesgas from a solenoid valve energized by a thermoelectric enerator throu ha main thermostat [21] Appl 334057 switch. In order $0 reduce the Eventemperature to,

Related US. Application Data 1 e.g. 170 F. to keep the food warm after atimer has [62] Division of Ser. No. 168,077, Aug, 2, 1971, Pat. No. downtime and a lfeep'wam thermostat 3,754,703 erate two sw1tches,respectlvely, to short circuit the solenoid or the thermoelectricgenerator periodically. 52 us. (:1. 307/117, 317/9 A The thermoelectricgenerator output is in the millivolt 51 Int. Cl. l-lOlh 47/24 g Thus,use of one or two additional, p [58] Field of Search 307/117, 118, 116,Siva, Series switches in the circuit can make Solenoid 307 112; 317/40 9R, 9 A operation unreliable because of even moderate contact resistance.Even the use of expensive gold 5 References Cited may not avoid theseries switch problem. The control UNITED STATES PATENTS assemblydisclosed herein avoids this problem by use of a disabling shunt insteadof a series switch. 2,217,785 10/1940 Betz et al. 307/117 UX 2,249,4427/1941 Thornberry 307/117 UX 2 Claims, 5 Drawing Figures PATENTEII IIIII 3.786.274

SHEET 2 F 2 ,24 s4 i r-" --b% A. THERMOSTATIC H THERMOELECTRIC 23ACTUATOR GENERATOR L7F3 VALVE 52 sOEENOIO Z WINDING 44 l9 FTHERMOSTATICI ACTUATOR I E FIG.5

24 T THER TA THERMOELECTRIC MOS T I GENERATOR -23 50 VALVE i7 sOEENOIOWINDING g AUTOMATIC WEI 58 l CONTROL APPARATUS BACKGROUND OF THEINVENTION This invention relates to electrical devices for energizationby the output voltage of a thermoelectric generator including-at leastathermopile, and more particularly, to a control assembly to deenergizesuch a device without opening the circuit between the device and thethermocouple. A

Although the device of the present invention will have considerableutility when used in connection with an oven for agas range in whichfood is cooked, the invention is not limited to this many otherapplication described herein. It will,.thus, have other usefulapplications. I

In the past, a thermocouple has been connected in series with'a mainthermostat switch and a gasrange. Thus, the thermocouple supplies anexciting voltage for the solenoid in the millivolt region. r

. It-is also old in the art to automatically reduce oven temperature bythe useof a timer; Typically, the temperature is reduced'to 170 F. tohold the food at serving temperature after it has cooked. However, ifattempts are made to do this electrically in a millivolt system byopening the circuit, additional series contacts must be used. Theaddition of additional series contact resistances can make the systemunreliable. The reliability problem canbe alleviated to some extent bythe use of gold or platinum contacts but this adds expense.

SUMMARY OF THE INVENTION In accordance with thedevice of the presentinvention, the above-described and other disadvantages of the prior artare overcome by short circuitinga thermocouple orthe load connectedthereto. In eithercase,

tendant upon the short circuiting of the thermoelectric generatoror theload. 1

By short circuiting, no extra pair of contacts are needed in series withthe thermoelectric generator. The

available E.M.F., therefore, remains high because additional contactresistance is absent. Further, inexpensive shorting contacts may beemployed because they need BRIEF DESCRIPTION OF THE DRAWINGS In thedrawings which are to be regarded as merely' illustrative:

FIG. 1 is a vertical sectional view through a gas oven;

FIG. 2 is a vertical sectional view of a portion of a thermostaticactuator;

FIG. 3,is a vertical sectional view of a portion of another thermostaticactuator;

FIG. 4 is a block diagram of one embodiment of the present invention;and

the. load is disabledll lowever, no disadvantages are at- I FIG. 5 is ablock diagram of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an oven is indicatedat having a housing 11. A pair ofbulbs 12 and 13 are fixed insidehousing 1 l. A pair of tubes 14 and 15 are connected from bulbs 12 and13, respectively. The interior of tubes 14 and 15 lie in communicationwith the interiors of bulbs 12 and 13, respectively. Junctions l2 and 13are thus hollow. Junctions 12 and 13 and tubes 14 and 15 are filled witha thermally expansible liquid. The manner in which bulbs 12 and 13 areused will be described hereinafter.

A partition 16 is fixed inside oven 10 to housing 11.

A main burner 17 is also fixed inside housing 11. A solenoid valve 18having a winding 19 shown in FIGS. 4 and 5 is connected from a gas inputconduit 20 at a pipe T 21. Inlet 20 is also connected to a pilot burner22. A thermoelectric generator 23 is located adjacent pilot burner 22 tobe heated by the heat of combustion, generated by gas burning a pilotburner 22. t .It is not conventional to employ two bulbs 12 and 13 andtwo tubes 14 and 15 in F IG.- 1. However, all of the apparatus shown inFIG. 1, except the two bulbs 12 and 13, and the two tubes 14 and 15 maybe entirely conventional.

Thennostats are shown at 24 and 25 in FIGS. 4 and 5. Thermostat 24includes bulb 12, tube 14, and all the structure other than tube 14,shown in FIG. 2. Note will be taken that tube 14 is connected to abellows 26 which operates a lever 27 biased by a spring 28. Lever 27 isfulcrumed on the end of a shaft 29 threaded through a housing 30. Therotatable position of shaft 29 is manually adjustable by a knob 31.

Repeated expansion and contraction of bellows 26 will cause repeatedopening of leaf spring contacts 32 and 33 of a switch 34 when the liquidin btilb 12 expands and contracts, respectively.

Bulb 12, tube 14 and all-ofthe structure shown in FIG. 2 may be entirelyconventional. The cooking temperature of theoven 10 may thus beset byturning knob 31 from zero to some baking temperature.

Thermostat 25 operates differently from thermostat 24. Thermostat 25includes bulb 13, tube 15 and all the structure connected from tube 15,shown in FIG. 3. Thermostat 25 includes a bellows 35, a lever 36 and aspring 37 which may be, if desired, identical to bellows 26, lever 27and spring 28. A set screw 38 is threaded through housing 39 to set thekeep warm" temperature of the oven. 1

The apparatus of FIG. 3 includes a switch 40 having leaf springcontacts'4l and 42 which are engaged when bellows expands. Thus, switchcloses when bellows 35 expands, whereas switch 34 opens when bellows 26expands.

As shown in FIG. 4, all of the structure of thermostat 24 is labeledthermostatic actuator at 43, with the exception of switch 34. Similarly,all of the structure of thermostat 25 is labeled thermostatic actuator"44, with the exception of switch 40.

Then'noelectric generator 23 has one lead 45 connected to ground at 46,and another lead 47 connected to switch 34.

Winding 19 has one lead 48 connected to ground at 46, and another lead49 connected to a junction 50.

Junction 50 is connected to both switch 34 and to a timer switch 51,timer switch 51 being operated by a timer 52.

The timer switch 51, in turn, is connected to thermostat switch 40, theother side of thermostat switch 40 being grounded at 53.

In the embodiment of FIG. 4, timer 52 is of the type that keeps switch51 open until it runs down to time ZERO. Switch 51 is then closed. Timer52 is also of the type which may be located from a ZERO position to anOFF position where switch 51 is open to turn the keep warm control off.

Inthe operation of the embodiment of FIG. 4, knob 31 is turned to thedesired cooking temperature. Actuator 43 then closes switch 34 until thetemperature inside housing 11 rises to the temperature set by turningknob 31. When the housing temperature rises above the set temperature,actuator 43 opens switch 34. When the temperature inside housing 11falls below the set temperature, actuator 43 closes switch 34, and soon. The foregoing is the operation with the timer 52 in the OFFposition. Should it be desired to bake at the set temperature for apredetermined time and then to reduce the temperature inside housing 11to, for example, 170 F., timer 52 is set to the baking time. Switch 51is thus kept open and baking occurs as previously described until thetimer 52 returns to the ZERO position. Switch 51 is then closed. Theactuator 44 has previously closed switch 40. The closure of switch 40short circuits winding 19 through switch 51 to ground. Thermostat thusacts as an override and lowers the temperature inside housing 11 to, forexample, 170 F. When the temperature inside housing 11 falls below 170F., the liquid inside bellows will contract sufficiently to open switchand remove the short circuit across winding 19. Thermostat 25 will thuskeep the temperature inside oven 11 at, for example, 170 F. until timer52 is turned to the OFF position.

As shown in FIG. 5, it is unnecessary to have a ground connection.Winding lead 48 may thus be connected to thermostat 25 by a lead 54,thermoelectric generator lead being connected to both leads 48 and 54 ata junction 55.

Although timer 52 may be entirely conventional, a timer 56 may also beemployed of a simpler nature, timer 56 also being conventional. Timer 56need not have an OFF position spaced from a ZERO position, as describedpreviously, in connection with timer 52. In this case, a single-pole,double-throw switch 57 is connected from junction 50 through a switch 58operated by timer 56 to thermostat 25. Thus, to shut off the keep warm,switch 57 is opened by switching to the manual position. Timer 56 thuskeeps switch 58 open at all times except when it is in the ZEROposition. In the ZERO position, timer 56 closes switch 58.

Both of the embodiments shown in FIGS. 4 and 5 are employed to shortcircuit winding 19. However, this is not necessary. That is, theinvention may be practiced also by simply short circuitingthermoelectric generator 23.

Note will be taken that switches 34, 51, 40, 57 and 58 may either bemechanical, solid state or other switches. That is, the same or similarreferences to stable states" herein and in the claims is hereby definedto include mechanical and/or electrical stable states.

What is claimed is:

l. A thermoelectric generator and a gas valve solenoid winding connectedin series circuit, temperature responsive means responsive to a firsttemperature for actuating a first switch, temperature responsive meansresponsive to a second temperature for actuating a second switch, meansconnecting at least one of said switches in parallel with one of saidgenerator and said solenoid winding for interrupting current in saidwinding when its temperature is exceeded and means converting the otherof said switches to interrupt the current in said winding when itstemperature is exceeded.

2. The combination of claim 1, including timer means connected in saidcircuit to cause the one of said temperature responsive means responsiveto the lower temperature to be ineffective when said timer is runningand to be effective after said timer has run.

1. A thermoelectric generator and a gas valve solenoid winding connectedin series circuit, temperature responsive means responsive to a firsttemperature for actuating a first switch, temperature responsive meansresponsive to a second temperature for actuating a second switch, meansconnecting at least one of said switches in parallel with one of saidgenerator and said solenoid winding for interrupting current in saidwinding when its temperature is exceeded and means converting the otherof said switches to interrupt the current in said winding when itstemperature is exceeded.
 2. The combination of claim 1, including timermeans connected in said circuit to cause the one of said temperatureresponsive means responsive to the lower temperature to be ineffectivewhen said timer is running and to be effective after said timer has run.